The present invention relates to a scroll-type fluid displacement apparatus which is adapted to compress, expand and pump-up a fluid and, more particularly, to a small-sized and closed scroll-type fluid displacement apparatus suitable for use as a refrigerant compressor for household electric appliances such as refrigerator, air conditioner or the like.
Scroll-type fluid displacement apparatus for treating fluids has been disclosed in, for example, the specification of U.S. Pat. No. 3,884,599 entitled "SCROLL-TYPE POSITIVE FLUID DISPLACEMENT APPARATUS", the specification of U.S. Pat. No. 3,924,977 entitled "POSITIVE FLUID DISPLACEMENT APPARATUS" and so forth.
In this scroll-type fluid displacement apparatus, two plates, each having a spiral wrap of a uniform height arranged on a flat surface, are disposed to oppose to each other, such that the upper end surface of the wraps are held in contact with the flat surfaces of the opposing plates. As one of the plates is rotated, the volume of a pocket defined by a pair of wraps and plates is changed to perform the displacement of a fluid. The principle of operation of this apparatus will be described with specific reference to FIGS. 1 to 4.
FIGS. 1 to 4 illustrate only a pair of wraps while neglecting the flat plates. Referring to these Figures, the scroll-type fluid displacement apparatus includes a stationary scroll wrap 1a, and a revolving scroll wrap 2a, with a discharge port 3 located in the vicinity of the center 0 of the stationary scroll wrap 1a. The center P of the revolving scroll wrap is adapted to revolve round the center 0 of the stationary scroll wrap 1a at a radius of R. A relative movement is performed such that the walls of the scroll wraps 1a, 2a are held always in contact and the point of contact is moved continuously. Closed fluid pockets 4 are formed by the positional relationship between two scroll wraps as stated above. To assist the understanding, one of the fluid pockets 4 is hatched in FIGS. 1 to 4. This fluid pocket 4 is moved from the radially outer extremity toward inside as the revolving scroll 2a rotates, as shown successively in FIGS. 1 to 4, to reduce its volume gradually. Therefore, the fluid in the pocket is pressurized to the maximum pressure in the state shown in FIG. 4, and is discharged to the outside through the discharge port 3. This apparatus can serve as a compressor, provided that means for maintaining a high pressure is disposed on the extension of the discharge port 3.
When this scroll-type apparatus is used as a compressor, the high pressure of the fluid established in the fluid pocket 4 acts to separate the rotary scroll from the stationary scroll. This force will be referred to as "axial force" hereinafter, because it acts in the same direction as the shaft such as crank shaft for rotatively driving the revolving scroll. For an efficient use of this apparatus as a compressor, it is necessary to employ suitable means for continuously applying a force counter-acting this axial force. In each of the stationary and rotary scrolls, the end portion of the scroll is maintaining a sliding contact with a mirror-finished surface of the opposing plate. It is, therefore, necessary to provide suitable sealing means for preventing the fluid from leaking through the portions of sliding contact.
FIG. 5 shows examples of the means for counteracting the axial force and sealing means at the ends of the scroll wraps 1a, 2a suitably used in the scroll-type compressor. More specifically, FIG. 5 is a sectional view showing an essential part of the scroll-type compressor. In this Figure, a stationary scroll 1 and a revolving scroll 2 having spiral wraps 1a and 2a, respectively. The revolving scroll 2 is adapted to be driven by a drive shaft 2c which is coupled to a crank shaft 7 through a bearing. The center of the drive shaft 2c is offset from the center of the crank shaft 7, so that the rotary scroll 2 revolves around the center of the stationary scroll 1 as the crank shaft 7 rotates. The crank shaft 7 is carried by the main frame 6 by means of bearings. A ring 11a having a key way and a key 11b in combination constitute rotation-prevention means adapted to prevent the revolving scroll 2 from rotating around its own axis, thereby ensuring the revolution of the same around the center of the stationary scroll 1. A suction and discharge ports 15 and 3 are connected to other components through pipes, so that the apparatus may function as a compressor.
In this scroll-type compressor, a thrust bearing 8 is disposed between the revolving scroll 2 and the crank shaft 7 to bear the aforementioned axial force. Namely, this thrust bearing 8 constitutes the means counter-acting the axial force. As the means for providing a seal between the ends of the scroll wraps 1a, 2a and the mirror-finished surfaces 5, there is provided a sealing means at the end of each scroll wrap 1a, 2a which includes: a groove formed in the end surface of each scroll wrap 1a, 2a; a sealing member 9 disposed in the groove and a biasing means 10 such as a cord made of an elastic member and adapted to press the sealing member 9 against the mirror-finished surface 5 of the opposing scrolls 1, 2.
The following problems are caused when this type of compressor is used as a comparatively small-sized compressor such as the compressor for household electric appliances.
Generally speaking, it is not practical to replace essential parts of domestic electric appliances. It is therefore necessary that the essential parts such as compressor operates for a long time without repair. However, the thrust bearing 8 bearing the axial force cannot fulfill this requirement because of the limited life of the lubrication. Thus, this arrangement cannot be practically used.
Also, the sealing means provided at the scroll wrap ends, constituted by the sealing member 9 and the biasing means 10, incurs various inconveniences such as increase of number of parts, difficulty in processing and so forth. Further, the sealing members and the biasing means are extremely small in the small-sized compressors resulting not only in the enhanced difficulty in processing but also in the necessity of replacement due to wear or distortion on the way of use. Thus, the conventional scroll-type compressor could not be practically used for domestic electric appliances.